Cast polyesterurethane rubbers



CAST POLYESTERURETHANE RUBBERS Charles E. Broclrvvay, Akron, Ohio, assignor to The B. F. Goodrich Company, New York, N. Y., a corporation of New York No Drawing. Application July 18, 1952,. Serial No. 299,760

6 Claims. (Cl. 260--30.6)

This invention relates to synthetic elastomeric polymers of the polyesterurethane class and to the preparation thereof; more particularly it relates to cured rubbery products prepared by the condensation of certain polyesters with organic diisocyanates, the addition of certain polyfunctional hydroxyl compounds as curing, agents, casting of the liquid mixture and subsequent heating to obtain elastic rubbery products of remarkable properties.

Reaction products of polymeric diols and organic diisocyanates that are liquid or fluid when warm can be prepared and cast into molds, so that on further treatment with heat, solid rubber-like products will be formed.

Such cured rubber-like materials are obtained by mixing.

in proper sequence and under appropriate conditions, for example, a hydroxyl terminated polyester and an organic diisocyanate to form a polyesterurethane and while this is still fluid adding a suitable polyfunctional curing agent and heating the fluid mixture in a mold of any desired shape to effect a cure.

I have now discovered, quite unexpectedly, that when the molar ratio of the reactants required to prepare a cast rubbery product are controlled within rather critical limits a cured elastic polyesterurethane withoutstandingly low hysteresis and permanent set values is obtained. For example, i am able to prepare by casting techniques and employing close control over the ratio of reactants, to be hereinafter set forth more fully, a cured rubbery polyesterurethane with a heat rise of only 1 F. when tested in the Goodrich flexometer at 212 F. with a 55 pound load and an 0.25 inch stroke, and: a. permanent set value of 0. This rubbery polymer is greatly superior to other present.- ly known synthetic rubbers because of low heat. buildup on deformation and negligible permanent set.

In accordance with this invention a method is provided for obtaining rubbery polymers of superior physicalproperties by casting techniques. In' the practice of this invention a predetermined amount of an organic diisocyanate is added to an anhydrous polyester which may contain a plasticizer and the mixture heated with agitation at a temperature sufiicient to cause reaction in a liquid state. A controlled amount of apolyfunctional hydroxyl material is mixed into the liquid, gas bubbles removed by evacuation if necessary, and the mixture poured into a mold and cured at such temperatures and times as are required to efiect a cure. The resulting product is a solid, tough, elastic, rubber-like product which exhibits very low hysteresis and permanent set and high tensile strength.

In order to achieve these results it is of critical impor- 2. tartce that the molar ratio of the reactants employed be carefully controlled. There must be a molar excess of the organic diisocyanate over the total mols of polyester and polyfunctional hydroxyl curing agent employed. The preferred quantities employed are one mol of polyester, more than 1.3 mols of organic diisocyanate and between 0.1 and 1 mol of the polyfunctional hydroxyl curing agent. The preferred. balance to be maintained between the re actants will be more fully disclosed in the examples given hereinafter. A preferred molar ratio is 1.0 polyester/ 1.5 organic diisocyanate/0.2 polyfunctional hydroxyl curing agent.

In the practice of this invention a preferred procedure is to melt together at about C. 1 mol of a hydroxyl terminated polyester, average molecular weight about 1300,

and 50 parts by weight, per Weight parts of polyester, of tricresyl phosphate; dry the mixture by degassing at about 1 mm. pressureand 90-100 C. for 10 minutes; add 1.5 niols' of p-phenylene diisocyanate to the molten fluid and. stir for 6 minutes at? 90 to' 95 C.; stir in 0.3 mol of glycerol for two minutes, and pour into a preheated mold which has been coated with silicone grease. The mold is then placed into an oven at. C. and cured for about 10 hours. The resulting cured product is a tough, rubbery, oil-resistant, oxidation resistant, material with a Goodrich hysteresis value of A1 F. at 212 F. and a permanent set value of 0.

The starting polyesters are prepared by an esterification condensation reaction of an aliphatic dibasic (dicarboxylic') acid or ananhydride thereof with a glycol. The preferred reactant-s are adipic acid and ethylene glycol. Polyesterswith terminal carboxyl or hydroxyl groups may be prepared by reacting a molar excess of the appropriate acid or glycol. Those polyesters with terminal hydroxyl groups are the most useful for the purposes of this invention.

The dibasic acid and glycol are reacted together by heating, preferably at about C. at atmospheric pressure for about 5 hours and while continuing to heat, the pressure is slowly reduced to about 1 mm. over a 10 to 15 hour period. During the initial heating period substantially all of the water of ,esterification and excess reactants. are removed and this may be facilitated by bubbling nitrogen through the mass. Polyesters of average molecular weights of 600 to 2000 are obtained in this way. By continuing. the evacuation and by heating the batch at higher temperatures, polyesters of molecular Weights in the range. of 2000 to 3000 or higher may be obtained. The polyester should be stored under anhydrous conditions it it isnotutilized at once. If anhydrous polyester is. not employed, bubbles may appear in the cured stock.

The polyester utilized includes polyesters prepared from the esterification of such dicarboxylic acids as malonic, succinic, glutaric, adipic, pimelic, sebacic, suberic, azelic, maleic and the like; It is not essential that the acid be used, the acid anhydride or acid chloride may be employed. Mixtures. of acids may also be used.

The glycols utilized in the preparation of the polyester by reaction with the dicarboxylic acid may be ethylene glycol, 1,3-bntanediol, 1,4-butanedi0l, pentamethylene glycol, hexamethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1:,3-propanediol, 1,2-butanediol and. the like; Mixtures of glycols. may be employed.

The preferred organic diisocyanate for reaction with the polyester is a phenylene diisocyanate such as p-phenylene diisocyanate, m-phenylene diisocyanate or 4,4'-diisocyanato dibenzyl. Other organic diisocyanates which are useful include such aromatic diisocyanates as naphthylene- 1,5-diisocyanate, diphenylmethane-p,p'-diisocyanate, triphenylmethane p,p diisocyanate, meta-tolylene diisocyanate, aliphatic diisocyanates such as hexamethylene diisocyanate, mixtures of diisocyanates and the like.

The molar quantities of diisocyanate employed in the permanently with polytetrafiuoroethylene or other nonpractice of this invention are. 1.3 to 2.0 mols per mol of adhesive material to avoid sticking of the casting to the polyester with 1.3 to 1.6 mols preferred. When molar mold. quantities above 1.6 are' employed harder products are The following examples are given to illustrate the pracobtained. The amount of diisocyanate employed must tice of the invention and more clearly to demonstrate its be greater than the molar sum of polyester and hydroxyll5 embodiments. containing curing agent. When the molar amount of polyester and curing agent is greater than the mols of di- EXAMPLES 1 1HROUGH 7 h o t d a soft stock of inferior 1 8;32 2? g gggg 18 b mm 0.03 86 mol (50 grams) of anhydrous hydroxyl termi- The polyfunctional hydroxyl curing agent is preferably 20 hated Polyethylene lf h an average molecular glycerol and other triols such as 1,1,1-trirnethylol pro- Welght of about 1300 1s We1ghed 1hto a S1de arm Erylhj Pane, trimethylolhexane, monoesters of pentaerythritol y flask and Parts y Welght g a of and the like. Low molecular Weight polyesters with terw Phosphate 15 added to the Polyester 1n the hash minal hydroxyl groups prepared from a dibasic acid, which 1s placed upon a hot plate that has a surface temcol and a triol are particularly useful for this purpose. 25 h h of about 120 A Veehhth o about mm The glycols or polyesters of the types listed hereinbefore 1S aPPhed o the e e e hhxture evaehatefi for may also be employed as Curing agents but the cure rate about ten minutes with intermittent swirllng. A welghed is much slower than that of a triol, such cures often have emouht (92ft grams o Example 4) Qt to be completed by ageing in the open atmosphere for rsocyanate, indicated in terms of molar ratio in Data several days. Mixtures of triols and diols result in cast Table L is added to the hqulod hhxtm'e whleh Shohlo be rubbery polyesterurethanes with a good balance of Physi at a temperature of about 90 and the mixture st1rred cal properties other polyfunctional hydroxyl agents for about 6 minutesv The indicated amount (0.48 gram such as ethanolamine, diethanolamine and the like are pl of ethylene glycol is then added to the very eltective curing agents. Ethanolamine, in fact, may mixture and the mlxture agam stlrreo lflgorouslytor o cause gelatin in the fluid mixture but may be employed minutes. If gas bubbles are present 1n the mixture it in small amounts, for example, or with glycerol Or ethyle o e degassed for o ththhte- The moltehmtxthte ene glycol to effect a tight rapid cure. The amount of 1s immedlatelypoured into preheated molds which have curing agbnt employed may be from 01 to 1 mol with been coated with a silicone 011. The castmgs are oven 02 to O5 molprbferre cured at 120 C. for 10 hours and aged for several days In the preparation of polyesterurethane castings bub- 40 i an Open atmosphere P e e out from the mold bles of gas often appear in the Solid cured product mgs and dynamic properties determined by means of the These bubbles may be eliminated by degassing the liquid Yerzley osclllograph and the B. Goodnchd'lexometer. reaction mixture under vacuum prior to Casting. T The cr1t1cal ratio of reactants required to obtain the cured may also be eliminated by adding an organic ester plasti- Product 71th supenor propertles readily apparent cizer to the reaction mixture. The use of Such a Plasti these data. Example 4 Illustrates the ratio most usefully cizer decreases the viscosity of the fluid and allows gas employed f ethylene glycol When a Stock of 1 hy bubbles to escape more rapidly, Al curing h cast teresis is desired. The following Data Table I shows the material in a closed mold in a press often solves this H1018 of reactants used and the Properties of the rubbery dificulty. product obtained.

Data Table I Mo] Ratio of Reaetants Properties of Cast Product-Flexometer, lbs., 0.25 stroke 212 F. Yerzley Example Resilience Polyethylp Phenyl- 77 F. Hardness Permanent ene ene Ethylene Durometer Hysteresis, Adipate Dllsoeya- Glycol A" AT, F. Percent nate 1.00 1.50 0.50 80.3 02 Blowout--. 1.00 1. 50 .40 88.2 62 2 2.96 1.00 1. 5o 30 37. 0 50 1. 12 1. 00 1. 50 20 88. 1 41 0. 00 1.00 1. 40 40 85.3 56 1.00 1.40 30 88.6 56 5 2.15 1.00 1.30 30 82.7 51 Melted The plasticizer used to aid in the elimination of gas bubbles may be any that is compatible with the liquid polyesterurethane such as diphenyl octyl phosphate and tri-cresy phosphate, polyester plasticizers, methyl phthalate, benzyl phthalate, benzyl sebacate, N,N, dibutyl benzene sulfonamide, phenyl naphthyl ketone, dimethyl naphthalene, o-nitro biphenyl, butyl diglycol carbonate, tetrahydro furfuryl adipate and the like. The most important requirement of the plasticizer is that it be compatible with EXAMPLES 8 THROUGH 19 A series of castings are prepared using essentially the is used for the curing agent in this set rather than ethylene glycol. The molar ratios of reactants employed are indicated in Data Table II. These samples are cured by heating at 120 C. for 1012 hours. A tight cure is obthe polyester, does not react with the diisocyanate and tained and no further ageing is required'for these samples.

Data Table II M01 Ratio of Re'eta-nts Pro erties of Oasis Product;Flexomet r, 551115., 0.25 stroke 212 F. Yerzley Example Resilient:

Polyethylp-Pheuyl- 77 F. Hardness Permanent ene one Glycerol Durometer Hysteresis, Adipate Diisocya- A AT, F. Percent nate acid and ethylene and propylene glycol, at a mol ratio of about 6 to 4 of glycol, with an average molecular weight of 1930 is reacted with p-phenylene diisocyanate for 6 minutes at to C., for two minutes with ethylene glycol and cast into a heated mold. This product has no bubbles and is fiuid enough to allow those forming during agitation to escape. The cured product, prepared by heating at 120 C. for 10 hours in an oven is free of bubbles. If the diiso-cyanate polyester reaction is conducted at -115 C. bubbles will be found in the cured product unless the reaction product is degassed just prior to pouring. The molar ratio of reactants is polyethylenepropylene adipate 1.0 mol, p-phenylene diisocyanate 1.5 mols, ethylene glycol 0.25 mol. The cured rubber product has outstandingly good physical properties.

The cured rubbery castings of this invention are particularly useful in mechanical goods applications where resistance to oxidation and certain chemicals, low permanent set and low hysteresis are required or desirable. Through the use of casting techniques the fluid uncured product may be cast into any form or shape, and may be poured directly into cavities and the like in metal or other articles and cured in situ, thus allowing easier assembly than in the case Where solid products must be introduced into difiicultly accessible areas.

Although I have described representative embodiments of the invention, I do not desire that it be limited solely thereto but only by the spirit and scope of the appended claims.

I claim:

1. A cured polyesterurethane casting having low hysteresis comprising the reaction product of an essentially hydroxyl terminated polyethylene adipate having a. molecular weight of about 600 to 2500 with 1.3 to 1.6 mols of a phenylene diisocyanate in the presence of 10 to 50 Weight parts per 100 weight parts of polyester of an organic plasticizer, and 0.1 to 0.4 mol of a. polyfunctional aliphatic hydroxyl curing agent consisting essentially of a triol, said amount of phenylene diisocyanate being at least 0.2 mol excess over the sum of said polyethylene adipate and said polyfunctional aliphatic hydroxyl curing agent.

2. A cured polyesterurethane casting having low hysteresis comprising the reaction product of one mol of a hydroxyl polyethylene adipate having a molecular weight of 600 to 2000 with 1.4 to 1.6 mols of a phenylene diisocyanate in the presence of 10 to 50 weight parts per 100 weight parts of polyester of an organic ester plasticizer, and 0.2 to 0.4 mol of a polyfunctional aliphatic hydroxyl curing agent consisting essentially of glycerol, said amount of phenylene diisocyanate being at least 0.2 mol excess over the sum of said hydroxyl polyethylene adipate and said polyfunctional aliphatic hydroxyl curing agent.

3. A cured polyesterurethane casting having low hysteresis comprising the reaction product of a hydroxyl polyethylene adipate of a molecular weight about 1300 with about 1.5 mols of p-phenylene diisocyanate in the presence of about 50 weight parts per 100 Weight parts of polyester of an organic phosphate ester plasticizer, and about 0.3 mol of glycerol.

4-. The process for preparing cured polyesterurethane castings which comprises reacting together by heating a mixture of one mol of an essentially hydroxyl terminated polyethylene adipate having a molecular weight of about 600 to 2500 with 1.3 to 1.6 mols of a phenylene diisocyanate in the presence of from about 10 to 50 weight parts per 100 weight parts of polyester of an organic plasticizer, adding thereto from 0.1 to 0.4 mol of a polyfunctional aliphatic hydroxyl curing agent consisting essentially of a triol and curing to a solid state, said amount of phenylene diisocyanate being at least 0.2 mol excess over the sum of said polyethylene adipate and said polyfunctional aliphatic hydroxyl curing agent.

5. The process for preparing cured polyesterurethane castings which comprises reacting together by heating a mixture of one mol of hydroxyl polyethylene adipate having a molecular weight of 600 to 2000 with 1.4 to 1.6 mols of a phenylene diisocyanate in the presence of from 10 to 50 Weight parts per 100 weight parts of polyester of an organic ester plasticizer, adding thereto .from 0.2 to 0.4 mol of a polyfunctional aliphatic hydroxyl curing agent consisting essentially of glycerol and curing to a solid state, said amount of phenylene diisocyanate being at least 0.2 mol excess over the sum of said hydroxyl polyethylene adipate and said polyfunctional aliphatic hydroxyl curing agent.

6. The process for preparing cured polyesterurethane castings which comprises reacting together by heating a mixture of one mol of hydroxyl polyethylene adipate having a molecular Weight of about 1300 with about 1.5 mols of p-phenylene diisocyanate in the presence of 50 weight parts per 100 Weight parts of polyester of an organic phosphate ester plasticizer, and adding thereto about 0.3 mol of glycerol and curing to a solid state.

References Cited in the file of this patent UNITED STATES PATENTS 2,424,884 Cook et al. July 29, 1947 2,620,516 Muller Dec. 9, 1952 2,621,166 Schmidt et al. Dec. 9, 1952 FOREIGN PATENTS 831,772 Germany Feb. 18, 1952 OTHER REFERENCES De Bell et 211.: German Plastics Practice, pp. 300-312, 1946. 

1. A CURED POLYESTERURETHANE CASTING HAVING LOW HYSTERESIS COMPRISING THE REACTION PRODUCT OF AN ESSENTIALLY HYDROXYL TERMINATED POLYETHYLENE ADIPATE HAVING A MOLECULAR WEIGHT OF ABOUT 600 TO 2500 WITH 1.3 TO 1.6 MOLS OF A PHENYLENE DIISOCVANATE IN THE PRESENCE OF 10 TO 50 WEIGHT PARTS PER 100 WEIGHT PARTS OF POLYESTER OF AN ORGANIC PLASTICIZER, AND 0.1 TO 0.4 MOL OF A POLVFUNCTIONAL ALIPHATIC HYDROXYL CURING AGENT CONSISTING ESSENTIALLY OF A TRIOL, SAID AMOUNT OF PHENYLENE DIISOCYANATE BEING AT LEAST 0.2 MOL EXCESS OVER THE SUM OF SAID POLYETHYLENE ADIPATE AND SAID POLYFUNCTIONAL ALIPHATIC HYDROXYL CURING AGENT. 